Coatings are applied to paper webs when it is desired to achieve certain specialized properties in the finished stock. Blade coaters apply the liquid coating material to the moving paper web by bearing a blade which runs the width of the web at an angle against the web and discharging the coating material onto the paper in advance of the blade.
It is important to obtain an even layer of the coating material on the paper web, or else the final stock may display blemishes or streaks when printed upon. As the coater blade may extend from 200 to 300 inches across the web width, apparatus have been developed which allow the adjustable application of pressure against the blade through a multiplicity of backing bar units held in a housing and urged against the coater blade. These backing bar units have been each threadedly mounted to the housing and individually adjusted to incrementally position the coater blade. However, the individually adjustable backing bar units present discontinuities, or instantaneous changes in elevation between adjacent units. These discontinuities can result in streaking or other unevenness in the applied coating, particularly at high web speeds.
What is needed is a backing bar assembly for a coater blade which may be continuously adjustably along its length to apply pressure against the blade without sudden changes.